Recently, three dimensional image display devices have been popularized and accordingly, numerous attempts have been made at watching virtual objects through such devices. In particular, a technology that allows a user to directly manipulate and touch a virtual object outputted (i.e., displayed) through a 3D image display device is more requested. To implement such a technology, the user must recognize at which location in actual place the virtual object is placed.
Because a sense of depth, i.e., a feeling of a user regarding to what degree the virtual object is projected to actual space or move into the display surface based on a display surface of the 3D image display device, or a sense of distance that the user feels about the virtual object displayed through the 3D image display device depends on a cognitive ability of an individual user, there is a limit that each user cannot but feel the sense of depth or distance differently.
In addition, it has a limit that all users are provided with the same sense of depth or distance only when the user himself or herself must conduct manual pre-calibrated work because 3D images are created by using optical illusion due to the difference between the views of left and right eyes of the user.